1. Field of the Invention
This invention relates to the field of scanning images, and more particularly to automatically adjusting the quality of scanned images.
2. Description of the Related Art
Electronic scanning of images is becoming more prevalent as an increasing number of paper processes are converted to electronic processes and as devices such as printers, fax machines, scanners, and copiers are integrated into a single device. Point of sale scanning is becoming increasingly popular to scan checks, lottery tickets, etc. in order to reduce labor-intensive processes related to handling paper copies. Scanning technologies are also becoming less expensive, which in turn contributes to the growing popularity.
As users become increasingly dependent on scanning technology, the reliability of scanning technology for producing an accurate electronic copy of an image, defined here as a “scanned image,” is critical. Near-zero maintenance for the life of a scanner is also highly desirable. In applications where scanners are used continually, such as point-of-sale (POS) applications, maintenance may disrupt the use of the scanners and is therefore undesirable.
FIG. 1 depicts one embodiment of a conventional scanning system 10. The illustrated scanner 10 includes a transport 12 where a document 14 to be scanned is placed. The transport 12 may be fixed or moving as the document 14 is scanned.
As the document 14 is scanned, an illumination source 16 projects light off the document 14 along a scan line 18. The emitted optical rays pass through an imaging lens 20 to an array of sensors 22, and are then converted to a digital signal using an analog to digital converter 24.
The digital signal is stored in a computer memory 26 in the form of a scanned image matrix 28, where each picture element, or “pixel,” along a scan line represents a column of the scanned image matrix 28. As the document 14 is scanned, the transport 12 moves the image such that the scan line 18 moves and a segment of the scanned document 14 is scanned creating a new row in the scanned image matrix. Alternatively, the document 14 is fixed on the transport 12, and the scan line 18 moves across the document 14. This routine is continued until the entire document 14 is scanned and an entire scanned image matrix 28 is created.
The information in the scanned image matrix 28 may be processed by a CPU 30 to form a processed image matrix 32, which is also stored in the memory 26. In one embodiment, elements of the scanned image matrix 28 are compared to a table assigned to each pixel 34 to determine a corresponding element in the processed image matrix 32. The table assigned to each pixel 34 is used to compensate for differences from one sensor to the next in the array of sensors 22 or for other slight differences between pixels in the scanning process. Values in the tables that are assigned to each pixel 34 are set during a calibration process. The calibration process will be discussed below with regard to FIG. 4.
In general, the quality of scanned images can be monitored using control points within the scanning system or by monitoring the quality of the scanned image by analyzing the document 14 after it has been converted to an electronic form using the processed image matrix 32. Monitoring control points, such as low toner, paper jams, hardware failures, etc., within the scanning system are common and can determine failures of the hardware and software components. Unfortunately, analyzing control points cannot detect many problems such as accumulation of dust and debris, optical or electronic defocus, malfunctioning sensors for picture elements (pixels), and other hardware problems.
Periodic maintenance by a technician may be able to detect problems that are not detectable through simply monitoring control points. However, periodic maintenance requires the scanning system to be taken out of use during the maintenance. Furthermore, periodic maintenance requires a technician to physically travel to the site where the scanner is located, which may involve a greater cost than a consumer is willing to bear for an inexpensive scanner. In contrast, if periodic maintenance is not performed, accumulation of dust or other problems will cause the scanner to produce a darkened or otherwise unacceptable image.
As mentioned above, the second method of monitoring the quality of a scanned image is to analyze the document 14 after it has been converted to an electronic form using the processed image matrix 32. A process for analyzing the quality of a scanned image to identify unacceptable images is described in U.S. Pat. No. 5,963,654 issued to Prakash, et al. on Oct. 5, 1999. However, this patent only looks at scanned images on a case by case basis, does not involve the correction of scanned images, and does not track image quality history.
What is needed is a process, apparatus, and system that automatically correct the image quality of a scanned image. Beneficially, such a process, apparatus, and system would decrease the frequency of expensive periodic maintenance.